This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-083409, filed Mar. 24, 2000; No. 2000-265737, filed Sep. 1, 2000, the entire contents of both of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a defect detecting apparatus for detecting macroscopic defects such as film thickness variations, contamination, pattern steps, and flaws on the surface of a semiconductor wafer substrate or a liquid crystal glass substrate.
2. Description of the Related Art
A surface defect detecting apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 9-61365 is a conventional apparatus for automatically inspecting substrates such as semiconductor wafer substrates and liquid crystal glass substrates. This apparatus illuminates the surface of an object to be detected and senses images of the regularly reflected light, diffracted light, and scattered light from the surface. In this way, the apparatus can detect film thickness variations, periodic disturbance of resist patterns, differences in sectional shape between resist steps, and the like by image processing. However, the surface defect detecting apparatus having this arrangement does not automatically optimize the angle of illumination and the like when sensing an image of the diffracted light. This makes defect inspection in an optimum state difficult to perform.
On the other hand, a method of automatically adjusting illumination for sensing an image of the diffracted light from a substrate such as a semiconductor wafer substrate or a liquid crystal glass substrate has been proposed. For example, a defect inspecting apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 10-339701 reads information concerning a pattern formed on a substrate, and checks whether the pattern is a periodic pattern. If the pattern is a periodic pattern, the apparatus receives the diffracted light and proceeds on to inspection. If the pattern is a line-and-space pattern, for example, the apparatus sets a rotational angle around the normal of the surface of the substrate such that the line direction is perpendicular to the incident direction of illuminating light. The apparatus calculates a diffraction angle xcex8d to the pattern pitch by an equation: sin xcex8dxe2x88x92sin xcex8i=mxcex/p, and sets the diffraction angle xcex8d obtained by this calculation as the angle of light reception.
However, in the apparatus which automatically adjusts illumination when sensing an image of the diffracted light as described above, the movement of an illuminating optical system is limited to a narrow range, so the incident direction of the illuminating light cannot be easily changed. Since this limits patterns which can be inspected by this apparatus, the apparatus cannot treat objects having various patterns.
Also, patterns formed on semiconductor wafer substrates and liquid crystal glass substrates are complicated, and have not only a kind of pattern pitch but also differ in pattern pitch according to portions on the substrate. Therefore, a good diffracted image cannot be necessarily obtained by the set diffracted light receiving angle. Furthermore, an optimum diffracted light receiving angle changes in accordance with the influence of a resist on the substrate and the like.
Conventionally, defects such as film thickness variations, periodic disturbance of resist patterns, and differences in sectional shape between resist steps on a substrate such as a semiconductor wafer substrate or a liquid crystal glass substrate are inspected by sensing an interference observation image of the substrate. This interference observation image is generated by interference between reflected light from the surface of a thin film (e.g., a resist film) formed on the substrate and light transmitted through the thin film and reflected from the substrate surface when illuminating light is irradiated to the substrate. To sense this interference observation image, illuminating light is made close to a single wavelength, or a bandpass filter is inserted before an image sensing device.
When an interference observation image is to be sensed, however, the interference conditions change in accordance with the conditions of a substrate such as the thickness and refractive index of a resist film, and the wavelength (observation wavelength) of illuminating light, so image sensing may not be performed under preferred conditions. As an example, an image saturates and makes it impossible to sense an interface observation image under favored conditions. Also, an apparatus which selectively interchanges a plurality of bandpass filters to change the observation wavelength selects the wavelength step by step. That is, the apparatus does not select a wavelength for performing image sensing under preferred conditions.
It is an object of the present invention to provide a defect detecting apparatus capable of setting to an optimum state the angle of at least one of an illuminating side and an image sensing side with respect to an object to be inspected, and capable of treating various objects.
A defect detecting apparatus for extracting a defect from image data obtained by sensing an image of an object to be inspected, comprising:
an illuminating unit which irradiates the object with illumination from a direction of predetermined angle;
an image sensing unit which senses an image of the object from the direction of predetermined angle;
an angle controller which controls an inclination angle of at least one of the illuminating unit and the image sensing unit;
an image processor which senses images of the object while the angle controller changes the inclination angle of at least one of the illuminating unit and the image sensing unit and obtains a relationship between each inclination angle and optical information corresponding to the each inclination angle; and
a determination unit which determines an image sensing condition suited to observation in accordance with the relationship between the inclination angle and optical information obtained by the image processor,
wherein the angle controller sets the inclination angle of the illuminating unit or the image sensing unit on the basis of a determination result from the determination unit such that the inclination angle matches the image sensing condition.
A defect detecting apparatus comprising:
an illuminating unit whose incident angle xcex8 changes with respect to a normal to a surface of an object to be inspected;
an image sensing unit which senses an image of light reflected by the object illuminated with the illuminating unit, the image sensing unit has an image sensing angle xcex8 changing with respect to the normal;
an image analyzer which extracts defect information from an image of the object sensed by the image sensing unit;
a determination unit which obtains an interference angle suited to interference observation on the basis of an observation wavelength and information concerning a film formed on the object; and
an angle controller which controls an inclination angle of the illuminating unit sand the image sensing unit on the basis of the interference angle obtained by the determination unit.
A defect detecting apparatus comprising:
an illuminating unit whose incident angle xcex8 changes with respect to a normal to a surface of an object to be inspected;
an image sensing unit which senses an image of light reflected by the object illuminated with the illuminating unit, the image sensing unit has an image sensing angle xcex8 changing with respect to the normal;
an angle controller which controls the illuminating unit and the image sensing unit such that an incident angle to the object is set equal to an image sensing angle;
an image processor which causes the image sensing unit to sense an image while the inclination angle of the illumination unit and the image sensing unit is changed by the angle controller, thereby obtains a relationship of a luminance value to the inclination angle; and
a determination unit which determines an optimum interference angle in accordance with the relationship of the luminance value to the inclination angle, which is obtained by the image processor,
wherein the angle controller controls the inclination angle of the illuminating unit and the image sensing unit on the basis of the interference angle obtained by the determination unit.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.